Variable-inductance coil having core threaded in coil form



061. s, 1963 HISAO MAEDA 3,106,691

VARIABLE-INDUCTANCE COIL HAVING CORE THREADED IN COIL FORM Filed May 24,1960 FigAVQAb INVEIV ORX Mzw United States Patent Office dflhfi lPatented Get. 3, 1963 3,105,691 VARIABLEHNDUCTANCE CUlllL HAVKNG CQRETHREADED EN (191i, FURM Hisao lvi'aeda, l3 Shiba-ltoen, Minatodtu,Tokyo-to, Eapan Fiicd May 24, 1960, Ser. No. 31,376 (Claims priority,application Japan May 25, 1959 3 Claims. (Ci. 336-4136) This inventionrelates in general to variable inductors and in particular to a new andimproved assembly of a hollow bobbin and a ferrite core forvariable-inductance coils.

It is an object of this invention to provide a bobbin forvariable-inductance coils wherein the disadvantages inherent inconventional bobbins of this type, as will be described hereinafter,have been eliminated.

It is another object of the invention to provide a bobbin forvariable-inductance coils, employing movable ferromagnetic core slugs,which has a simple, yet strong, construction adaptable to andreproducible in mass production with a high degree of uniformity.

The manner in which the foregoing as Well as other objects andadvantages may be best achieved will be understood more fully from aconsideration of the following description of one representativeembodiment of the invention, taken in conjunction with the accompanyingdrawing in which:

FIG. 1 is an elevational view, in longitudinal section, of a bobbinembodying the invention;

FIG. 2 is a cross-sectional view of the bobbin of FIG. 1 having a wedgemember attached to it;

FIG. 3 is an elevational view of one example of a ferrite core to befitted into the bobbin of FIGS. 1 and 2;

FIG. 4 is a plan view of the core of FIG. 3; and

FIGS. 5a and 5b are a perspective and a cross-sectional view of theWedge member of FIG. 2, the latter being taken along the line VBVB ofFIG. 5a.

In FIG. 1, the hollow bobbin cylinder or coil form 1 of the embodimentis made of a hard insulation material such as a hard synthetic resin andhas one or more slots 2 cut in the longitudinal direction. Said slots 2are adapted to receive the shank portion of one or more wedge-shapedbodies 3 which are made of a substance such as styrene, vinyl chloride,or other relatively soft insulating material, and which are providedwith integrally formed flanges 4 of curved configuration and relativelyreduced thickness for intimately contacting the outer surface of thebobbin cylinder 1. The member 3, or each of several such members, has ashank 3 adapted partly to protrude into the interior of the bobbincylinder it upon insertion and to be held firmly thereto by the coil Cwound about the bobbin cylinder 1.

In assembling the bobbin of the invention with an inductance-adjustingferrite core Fe shown in FIGS. 3 and 4, the said core Fe is screweddirectly into the bobbin interior, the outer screw threads of the coreFe thus cutting into and tapping the pliable, wedge-shaped member ormembers 3, whereby an extremely firm fitting is obtained between themating parts.

The bobbin of this invention enables inductance adjustments to be madeby causing the ferrite core Fe to move within the bobbin interiorthrough the action of conventional threads on the outer surface of thesaid core. This bobbin has the further advantage of tight fit even if acertain dimensional difference exists between the inner diameter of thebobbin cylinder 1 and the outer diameter of the core Fe because thewedge-shaped member or members 3 have pliability. Moreover, it ispossible to obtain a higher Q value than in the conventional corewherein a metal screw is used because the inner diameter of the bobbincylinder 1 can be made closer to the outer diameter of the core Fe.

Furthermore, the bobbin of the invention has the advantage of beingeasily fabricated, there being no neces sity of carrying out thedifiicult process of cutting precise screw threads on the inner surfaceof the bobbin cylinder made of hard insulation material, and there beingonly the necessity of cutting a slot, or slots, 2 in the bobbin cylinder1 in the longitudinal direction. It is a special feature of theinvention that, since the flange 4 of the member 3, on the outer surfaceof the bobbin cylinder 1, is held fast by the coil C wound about thesaid bobbin cylinder, the member 3 is fastened securely to the saidbobbin cylinder, and the core Fe yielda-bly but positively engagedthereby is held securely in its selected axial pos tion relative to thecoil whereby stability of operation 1s insured.

Although this invention has been described with respect to a particularembodiment thereof, it is not to be so limited as changes andmodifications may be made therein which are within the full intendedscope of the invention, as defined by the appended claims.

What I claim is:

1. A variable-inductance coil comprising a tubular coil form ofrelatively hard electrically insulating material provided with at leastone longitudinal slot, a body of relatively soft electrically insulatingmaterial engaging said slot and projecting therethrough into theinterior of said form, said body having a flange thereon positivelyengaging said form and being held against inward radial displacement bysaid flange, said flange extending generally parallel to the axis ofsaid form while overlying the periphery thereof, wire-coil means woundaround the periphery of said form and said flange, thereby securing saidbody in said slot, and a core threaded into the interior of said form inengagement with said body.

2. A variable-inductance coil comprising a tubular coil form ofrelatively hard electrically insulating material provided with at leastone longitudinal slot, a generally T-shaped body of relatively softelectrically insulating material having a shank portion engaging saidslot and projecting into the interior of said form therethrough, saidbody further having a flange portion engaging the periphery of said formand held against inward radial displacement therein, wire-coil meanswound around the periphery of said form and said body, thereby securingsaid body in said slot, and a core threaded into the interior of saidform in engagement with said body.

3. A variable-inductance coil comprising a tubular coil form ofrelatively hard electrically insulating material provided with at leastone longitudinal slot, a generally T-shaped body of relatively softelectrically insulating material having a shank portion engaging saidslot and projecting into the interior of said form therethrough, saidbody further having a flange portion engaging the periphery of said formand held against inward radial displacement therein, wire-coil meanswound around the periphery of said form and said body, thereby securingsaid body in said slot, and a core threaded into the interior of saidform in engagement with said body, said flange portion bearingexternally upon said form and having a thickness substantially less thanthat of said form.

References Cited in the file of this patent UNITED STATES PATENTS2,838,738 Antalek June 10, 1958 FOREIGN PATENTS 193,453 Switzerland Mar.1, 1938

1. A VARIABLE-INDUCTANCE COIL COMPRISING A TUBULAR COIL FORM OFRELATIVELY HARD ELECTRICALLY INSULATING MATERIAL PROVIDED WITH AT LEASTONE LONGITUDINAL SLOT, A BODY OF RELATIVELY SOFT ELECTRICALLY INSULATINGMATEIRAL ENGAGING SAID SLOT AND PROJECTING THERETHROUGH INTO THEINTERIOR OF SAID FORM, SAID BODY HAVING A FLANGE THEREON POSITIVELYENGAGING SAID FORM AND BEING HELD AGAINST INWARD RADIAL DISPLACEMENT BYSAID FLANGE, SAID FLANGE EXTENDING GENERALLY PARALLEL TO THE AXIS OFSAID FORM WHILE OVERLYING THE PERIPHERY THEREOF, WIRE-COIL MEANS WOUNDAROUND THE PERIPHERY OF SAID FORM AND SAID FLANGE, THEREBY SECURING SAIDBODY IN SAID SLOT, AND A CORE THREADED INTO THE INTERIOR OF SAID FORM INENGAGEMENT WITH SAID BODY.